1. Field of the Invention
This invention relates generally to additives for engine fuels and lubricating oils. More specifically, this invention relates to combustion-optimizing additives for engine fuels and to anti-friction additives for lube oils that are less toxic than conventional additives.
2. Related Art
Overbased sulfonates are metallic salts of sulfonic acid compounds and are well known in the art. Overbased sulfonates are "characterized by a metal content in excess of that which would be present according to the stoichiometry of the metal and the acidic organic compound reacted with the metal". (Burke. Jr. et al. U.S. Pat. No. 5,259,966.) The "overbased" metal content of an overbased sulfonate typically may be suspended or complexed with the petroleum sulfonate. (Kirk-Othmer Encyclopedia of Chemical Technology, John Wiley & Sons, Third Edition, N.Y. (1979), vol. 22, page 23).
The most widely-used overbased alkaline-earth sulfonates are based on calcium, magnesium, and barium. (Kirk-Othmer, supra., vol 22, page 23). Overbased calcium sulfonates, for example, might include CaO, Ca(OH).sub.2, or CacO.sub.3 suspended or complexed with the sulfonate. For example, the formula for an overbased calcium petroleum sulfonate named C400-C.TM. manufactured by Surpass Chemicals Limited, West Hill, Ontario, Canada, is reported to be: (RC.sub.6 H.sub.4 SO.sub.3).sub.2 Ca+CaCO.sub.3.
Methods of manufacturing overbased sulfonates are described in various patents, including: Eliades et al., U.S. Pat. No. 4,129,589; Allain et al., U.S. Pat. No. 4,306,983; Allain et al., U.S. Pat. No. 4,347,147; Eliades et al., U.S. Pat. No. 4,597,880; Muir, U.S. Pat. No. 4,617,135; and Burke, Jr. et al., 5,259,966.
The extent to which an overbased sulfonate is "overbased", or "superbased" as described by some references, is described by: a) the metal ratio of equivalents of metal to equivalents of sulfonic acid, and/or b) by a measure of alkalinity (alkalinity value or titratrable base number). Titratable base number (TBN) is determined by titration and is equivalent to the milligrams KOH per gram of sample. (Kirk-Othmer, supra., vol. 22, page 23). Eliades et al. '589 discloses a method for producing an over-based oil-soluble magnesium salt of a sulfonic acid that exhibits metal ratios of up to 40 or more. Muir discloses a method for producing overbased magnesium sulfonates of exceptionally high alkalinity of up to 500 TBN or more.
Overbased sulfonates have been used in the past in lubricant fluids such as motor-oil additives and greases because of their excellent detergent and dispersing properties and their ability to neutralize engine acids. (Kirk-Othmer, supra., vol. 22, page 23, and vol. 14, page 494). Eliades et al. '589 discusses overbased, oil-soluble magnesium salts of sulfonic acids as lube oil additives that "function as detergents and acid neutralizers, thereby reducing wear and corrosion and extending the engine life."
An example of the use of overbased sulfonates in motor oil is disclosed by Arndt (U.S. Pat. Nos. 4,557,841 and 4,664,821). Arndt discloses a crankcase motor oil additive concentrate for addition to used engine oil to supplement and enhance the additive system already present in the used oil. Arndt's concentrate comprises 1) a petroleum base stock suitable for crankcase motor oils, 2) detergent-inhibitor package, 3) supplemental anti-wear additive from salts of dialkyl dithiophosphoric acid, 4) supplemental anti-wear additive from the class of sulfurized olefins, 5) corrosion inhibitor from the class of overbased sulfonates, the sodium salt being preferred, and 6) a lubricity additive known familiarly as jojoba oil. Arndt claims percentages of overbased sulfonate and jojoba oil in the concentrate of 1-5 wt-% and 0.1-10 wt-%, respectively, and percentages of the concentrate in the crankcase oil of 5-15 wt %.
Early overbased sulfonates, of the type used for engine crankcase oil, were sometimes added to straight oils for metalworking applications such as drawing and stamping. However, this use of the early overbased sulfonates was somewhat limited due to the need for development of overbased sulfonates with improved metalworking oil properties, including: better anti-corrosion properties, improved solubility in paraffinic base oils, lower viscosity for easier handling, better clarity when using the crystalline form of overbased sulfonates, reduced instability due to reactivity with other additives, and consistent lubricity in finished formulations. ("Alternatives for Chlorinated Paraffins in Drawing and Soluble Oils," Witco Corporation marketing brochure, April 1994).
Over the last few years, the use of overbased sulfonates in metalworking lubrication applications has become more common. This increased metalworking use results from improved overbased sulfonate formulations and because of interest in removing chlorinated paraffins from cutting and other metal-working oils because of environmental concerns about hydrogen chloride and hydrochloric acid.
New overbased sulfonate formulations have recently been developed in an attempt to broaden the applications of overbased sulfonates in metalworking. These formulations claim improved anti-corrosion properties and lessened reactivity with other additives, and therefore are valuable in many metalworking applications, such as press oils and prelubes. (Witco, supra.)
Overbased sulfonates for metalworking applications have been formulated from natural-based organic compounds, natural-synthetic-blend compounds, or synthetic-based compounds. Either natural or natural-synthetic blends are usually preferred because of the benefits of broad molecular weight distribution in most sulfonate applications. (Witco, supra.)
Overbased sulfonates used in engine oil and for metalworking have typically included alkaline-earth metals that are in amorphous form, which, in some cases, has limited their applications. For example, amorphous overbased calcium sulfonates have usually been used in metalworking as straight oils, without being emulsified in water, because contact with water thickens the sulfonate when the calcium amorphous form converts to the calcium crystalline form. Crystalline forms of overbased calcium sulfonate have recently been developed, in which the calcium is converted to the crystalline form in a controlled fashion during manufacture. (Witco, supra.) These crystalline overbased calcium sulfonates are recommended for metalworking applications where soluble-oil emulsions are needed, because they do not thicken with contact with water.